Here's my story when my '98 started losing power and performance right at 85k miles. First it was a bad cam position sensor that I couldn't diagnose. So it went to my indy and he got it back on the road again for me. But it never really ran as crisp and strong as before. It felt sluggish from light to light, not the way I remembered my car being when I first drove it off the showroom back in '97. I diagnosed much of my discontent to the vanos seal going out, in conjunction w/ the front suspension going bad as well. These two issues dropped the fun factor out of driving my car so much, that when my car hit 90k miles, I contemplated driving it to the nearest dealer and just trading it in. But I didn't do that, and at 97k miles, I decided to make a sizable investment and fix it up to be stone cold reliable and to last another decade (plan was to pass this car to my son when he turned 16). I put my car up on jack stands for 4 months, and proceeded to replace all parts that needed replacing, and while I was there, do preventive maintenance and replace stuff that will eventually fail. In 3 months, i spent ~$5500 on new maintenance parts. I DIY everything, put in about 140 hrs labor. Then once the car was back on the road, I bought a new hood, front bumper, headlights, fog lights, new wheels and tires
. That added another $3500 to the bill, totaling ~$9000. That was 2 yrs ago, my 528 was @ 98k miles.
Today, it's @ 116k miles, and the only thing I've had to do to it (other than 2 oil and filter changes) was to replace a set of sunroof rails (that I had broken back in '09 when I tried to DIY). Mechanically speaking, practically 90% of everything under my hood consists of all new parts since 2 yrs ago. As such, I don't expect to need to do or maintain anything under the hood for another 3 yrs. It was pretty painful seeing my CC bill rack up $9k on a car that's only worth $4k, but the pain was short and quick. The payback, however, proved to be worth it. I have another 3 yrs ahead of me where I feel very confident that nothing will need to be attended to before insp 2.